(Health.com) -- If you're wondering why you're tired after a full night's sleep, or jittery even without a venti latte, the answer might be on your plate.

"Marginal nutritional deficiencies may make you feel 'under the weather,'" says Elizabeth Somer, R.D., author of "Eat Your Way to Happiness." And eating too much of the wrong things can have the same effect, she says.

So if you haven't been functioning at 100%, try these foods to give your well-being a big boost.

Feel like every day is a slog? You may not be getting enough iron. Add in the fact that you lose the mineral when you menstruate, and you may feel groggy and fuzzy-headed even if you don't have a full-blown deficiency.

The remedy: Eat more red meats, fish, and poultry -- the best animal-based sources of iron. (Liver contains one of the highest amounts, too, but steer clear if you're pregnant, since its high vitamin A content may be dangerous to a developing baby.)

Don't eat meat? Go for soybeans, lentils, spinach, and fortified cereals. Iron isn't as easily absorbed by your body in those forms, but adding vitamin C will help, so enjoy a glass of OJ with those cornflakes.

If you tend to have heavy periods, you're probably losing more iron than the average woman, so be extra sure you're eating plenty of iron-rich foods, adds Carol Haggans, R.D., scientific and health communications consultant with the National Institutes of Health (NIH).

You know that caffeine can put you on edge. But here's another source of jitters: too many refined carbs -- foods high in white flour (cookies, sugary cereals, white bread, etc.) and stripped of nutrients and fiber that normally keep your blood sugar stable.

"A big dose of refined carbs causes your blood sugar level to soar and an excessive amount of insulin to be secreted by the pancreas," says Alyse Levine, R.D., nutrition advisor for Livestrong.com.

You may be antsy as a result: think toe-tapping and/or an inability to focus. Then, the extra insulin will make your blood sugar plummet, Levine explains, leaving you feeling sluggish.

To help prevent those drastic spikes and drops in blood sugar, Levine says, your meals and snacks should be based around lean protein, healthy fats, and unrefined carbohydrates. That means loading up on brown rice, whole-grain bread and pasta, whole oats, and, of course, fruits, veggies, and legumes.

So you misplaced your car keys. Again. A lack of omega-3 fatty acids and vitamin B12 -- both brain-boosting nutrients -- could be to blame.

"Omega-3s are loaded with DHA, a type of fatty acid that helps promote well-functioning synapses," says Joseph Quinn, M.D., associate professor of neurology at Oregon Health and Science University in Portland. Translation: It keeps neurons in your brain firing more effectively.

A lack of B12, meanwhile, has been linked with confusion, numbness, and fatigue. Up to 15% of Americans could be low on B12, according to the NIH, in part because some people may have trouble absorbing the nutrient. Get your brain back on track by chowing down on fatty, omega-3-rich fish like mackerel, trout, herring, tuna, and salmon.

To get more B12, try fortified breakfast cereal (many have 100% of the recommended daily value), liver, cooked clams, yogurt, cheese, whole eggs, and ham, as well as fish like salmon and trout.

If you're upping your intake of these foods and still feel disoriented, ask your doctor if you should consider having your B12 level tested, Haggans says.

Yes, veggies and legumes are great for you. But certain ones -- like beans, broccoli, cabbage, and cauliflower -- can produce lots of gas, leaving you with major bloat. (The jury's still out as to why, but their complex sugars may be difficult to digest.)

Carbonated drinks can also increase bloat, both because they're bubbly and because their artificial sweeteners can be hard for your body to break down. If your belly's feeling swollen, try halving the amount of bloat-boosting veggies you normally eat for a week to see if that helps.

Don't cut them out completely, though, because they provide crucial nutrients, says Roshini Rajapaksa, M.D., Health magazine's medical editor and a gastroenterologist and internist at the New York University Langone Medical Center/Tisch Hospital.

Ditch soda and seltzer, but keep drinking flat water, which helps relieve constipation -- another cause of the big B. Taking probiotic supplements may help, too; talk to your doctor about which one might be right for you.

It's normal to feel a little achy after a tough workout, but cramps could mean you're low on electrolytes like potassium or magnesium, Haggans says.

Potassium, for example, works with sodium to keep muscle contractions in check, so if you sweat it out, you may also have to deal with some pain in your calves or feet.

Your food Rx: While bananas are the most famous source of potassium, you actually get twice as much of the mineral from a medium-size baked potato. Prunes and orange juice have lots of it, too.

As for magnesium, go for almonds and most other nuts, greens like spinach, and bran flakes and other unrefined grains. Consuming calcium also helps; get it from low-fat milk, tofu, and dark, leafy greens like collards. Dehydration can cause cramps, too, so don't forget to keep chugging H2O.